September 29, 2011
Mercury Has Widespread Flood Volcanism
NASA announced on Thursday that its MESSENGER spacecraft has found new evidence that flood volcanism has been widespread on Mercury.
New data from the spacecraft reveals that 6 percent of Mercury's total surface is covered by volcanic plains."Analysis of the size of buried ℠ghost' craters in these deposits shows that the lavas are locally as thick as 2 kilometers" (or 1.2 miles), James Head of Brown University, the lead author of one of the reports published in Science, said in a press release. "If you imagine standing at the base of the Washington Monument, the top of the lavas would be something like 12 Washington Monuments above you."
Head said the deposits appear typical of flood lavas, containing huge volumes of solidified molten rock similar to those found in the Columbia River Basalt Group.
"Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents," Head said in a press release.
Scientists also discovered vents that measure up to 16 miles in length and appear to be the source of some of the tremendous volumes of very hot lava that have rushed out over the surface of Mercury.
Other analyses of the new data from MESSENGER also shows the first close-up views of Mercury's "hollows", the first direct measurements of the chemical composition of Mercury's surface, and the first global inventory of plasma ions within Mercury's space environment.
MESSENGER's orbital missions has provided new views of bright crater deposits that have been made scientists wonder what they are, until now.
"To the surprise of the science team, it turns out that the bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters," David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, and lead author of one of the Science reports, said in a press release. "The science team adopted the term ℠hollows' for these features to distinguish them from other types of pits seen on Mercury."
Hollows have been found over a wide range of latitudes and longitudes, suggesting they are common across Mercury.
Blewett said the ones detected so far have a fresh appearance and have not accumulated small impact craters, which shows these are very young.
"Analysis of the images and estimates of the rate at which the hollows may be growing led to the conclusion that they could be actively forming today," Blewett said in a press release. "The old conventional wisdom was that ℠Mercury is just like the Moon.' But from its vantage point in orbit, MESSENGER is showing us that Mercury is radically different from the Moon in just about every way we can measure."
Image 1: Moon—Mercury image comparison. (Left) The near side of the Moon, showing the dark volcanic areas (maria) composed of lava flows and the bright, heavily cratered highland crust. (Right) Mariner 10 view of Mercury showing that, unlike the Moon, there is no brightness contrast between the cratered terrain and the smooth plains. The Moon is about one-quarter of the diameter of Earth; Mercury is about one-third of the diameter of Earth. Credit: Lick Observatory (left); NASA/Jet Propulsion Laboratory/U.S. Geological Survey (right)
Image 2: Lava flows on Mercury more than 3.5 billion years ago – a mile deep in places – would have covered nearly 60 percent of the continental United States. The discovery was made by data returned from NASA´s MESSENGER mission to Mercury.
Image 3: Here a high-resolution monochrome image has been combined with a lower-resolution enhanced-color image. The hollows appear in cyan, a result of their high reflectance and bluish color relative to other parts of the planet. The large pit in the center of the crater may be a volcanic vent, from which the orange material erupted. Credit: Courtesy of Science/AAAS
Image 4: A View Looking Down on the North Pole of Mercury (Center). Credit: Courtesy of Science/AAAS and Brown University
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